1. Field of the Invention
The present invention relates to a method of recycling a disk recording medium which has a layered structure including a substrate, a dye layer, a reflective film, and a protective layer.
2. Description of the Related Art
Disk recording media, such as optical disks, have been widely used, for example, for recording music, images, and information because of their capability of high-density recording. In particular, compact disks (CDs) and other optical disks in the CD family have been used on a large scale.
Under the present circumstances, with regard to the issue of waste, the recycling of optical disks such as compact disks is being investigated. Most optical disks on the market are read-only type, such as CDs. As shown in FIG. 1, for example, a CD includes a polycarbonate substrate L3, an aluminum reflective film L2, and a protective layer L1 deposited in that order.
In a conventional method of recycling disks, disks are crushed as they are and molded. In such a case, the components of the protective layers and reflective films are also mixed into the molded product. It is not possible to recover the reflective films only, and the molded product is not transparent. Thus, the molded product is applicable only for limited usage.
In another method, disks are immersed in an acid or an alkaline solution to dissolve aluminum reflective films, thereby protective layers and substrates are separated from each other, and thus, the substrate resin is recycled. In this method, the recycled substrates are transparent and can be reused in a relatively wide usage, however, it is difficult to recover reflective films.
Apart from the read-only disks, recordable optical disks are also on the market. Although there are several types that are recordable, the present invention relates to optical disks which have a layered structure, as shown in FIG. 2, including a substrate L7, a dye layer L6, a reflective film L5 and a protective layer L4. Generally, in this type, recording is allowed only once. An example of this type is a CD-R (recordable compact disk). The CD-R includes, for example, a polycarbonate substrate, additives such as an organic dye, for example, a cyanine dye, and a quencher, a gold reflective film, and an ultraviolet-curable resin such as an acrylic resin.
Also, there is a DVD-R (recordable high-density recording disk: digital video disk), in which two layered structures described above are laminated together by means of, for example, an adhesive as shown in FIG. 3. That is, protective layers L11 and L11 are adhered together with an adhesion layer B. and a dye layer L9, a gold reflective film L10, and a protective layer L11 are deposited on a substrate L8 in that order on both sides. In these types of disks, in addition to substrates, expensive gold reflective films are used, and thus, the recovery of reflective films has been desired. For that purpose, although it may be possible to use a solution which dissolves reflective films as described above, only an extremely hazardous solution, for example, aqua regia, can be used. Also, by treating the whole disks at high temperature, organic substances such as substrates are burnt and gold only can be recovered, however, in this method, the substrate resin cannot be recovered.
The optical disks described above, shown in FIG. 2 and FIG; 3, have a layered structure including substrates, dye layers, reflective films, and protective layers. There is a need for recovering the substrates, the dye layers, and the reflective films separately. In particular, if the dye components of the dye layers are not recovered separately from the substrates, the resinous substrates cannot be recycled.